The subject invention is directed toward the art of pipe joints and couplings and, more particularly, to a flange-type pipe joint incorporating an improved relationship between the flanges and an associated gasket.
Flange-type pipe joints having elastomeric gaskets sealingly clamped between opposed flange end faces are frequently used in processing systems wherein fluid entrapment is highly undesirable. To reduce the likelihood of fluid entrapment, it is known to design the gasket and associated flanges such that when the joint is made up, the radially inner face of the gasket forms a smooth continuation between the interior surfaces of the connected pipes. Joints of this general type are shown, for example, in U.S. Pat. Nos. 3,775,832, 4,735,445, and German Patentschrifts CH 674764 A5 and 947,034.
The prior art has proposed various methods or designs to assure that over or under compression of the gaskets can not occur. In spite of this, the inventors of the subject invention have found that with many elastomeric gasket materials, repetitive temperature cycling can produce permanent extrusion of the inner periphery of the gasket into the flow path over a period of time. Even a slight extrusion can result in retention of substantial fluid in the pipe line. This can be a significant and often unrecognized problem in systems requiring high degrees of cleanliness and/or ease of flushing and changeover between different process fluids.